Requirements and Types of Building Foundations

The Regulations, requirements and different types of building foundations

Every country has a general set of Building Regulation Standards that has to be strictly imposed when designing and constructing any form of structure. The building standards are necessary to ensure that any construction made is safe for human occupancy and for people around the construction. Of late, a clause that a building has to be energy efficient for conservation and that it should have access to and about the building have been included.

In the UK, Building Regulations are divided into sections to deal with the various aspects of building construction.

UK Building Regulations

Part A - Structure

Part B - Fire safety

Part C - Site preparation and resistance to moisture

Part D - Toxic substances

Part E - Resistance to the passage of sound

Part F - Ventilation

Part G - Hygiene

Part H - Drainage and waste disposal

Part J - Combustion appliances and fuel storage systems

Part K - Protection from falling, collision and impact

Part L - Conservation of fuel and power

Part M - Access to and use of buildings

Part N - Glazing - safety in relation to impact, opening and cleaning

Part P - Electrical safety

Each building that has to be erected or extended, inclusive of other special constructions, must comply with the strict building regulations. Part A- Foundation may well be the "foundation" of the Building Regulations as a structure's footing and foundation system is its core base.

What is a Foundation and its Requirements?

The foundation is the structural component that transfers load from the building to the supporting ground. The supporting ground could be soil, rock or seabed. The foundation basically holds the building up so it will not sink to the supporting ground. It also holds the structure so it will not be blown away by strong winds like tornadoes. Whole houses being sucked up by tornadoes is not a make-believe story. The stories are true and the core problem was the foundations were not deep and strong enough.

The basic requirement for any structure regarding its loading is that the building shall be constructed in such a way that the combined dead and live loads together with the projected wind load can be carried and transmitted to the ground safely and without any deflection or structural damage. The second requirement is that any ground movement such as swelling, shrinkage, freezing or land-slip should not impair the stability of the building.

The code mandates that all foundations be located centrally under the wall. FOr foundations that are under chemically harsh conditions, a special concrete mix is recommended. For foundations under normal soil conditions, a regular 50 kg. Portland cement with a mixture 200 kg of fine aggregate and 400 kg of course aggregate will be fine. Most contractors are well-versed with these provisions. The required minimum footing (T) is 150 mm or 6 inches. The width of the foundation footing depends on the type of soil the foundation will rest and the load as expressed in k/N per linear meter. To make it simpler, the usual concrete foundation size to be poured on a slightly dense ground is 400 mm by 400 mm by 160 mm. Of course the size will vary accordingly with the increase in building height and capacity.

Reinforced concrete is a different application. Computations are done by structural engineers for high rise buildings for the proper size of foundations and the size and number or reinforcement bars as stiffeners. Concrete is compressive strength while a reinforcement bar is tensile. The two work together for a stronger composite.

Different Types of Foundation

There are so many names and types applied to foundations. However, there are only two basic types according to the depth of a foundation: deep and shallow. Deep foundations are used for high rise buildings. The depth is almost as half the height of the building itself and piles are embedded before finally pouring the foundations. Shallow foundations are only about 1 to 2 metres in depth and mostly used in the construction of one to four storey buildings. A seismic isolation foundation is also used for earthquake proofing a building. This type does not have a 100% guarantee but the seismic foundation will greatly help a building constructed in an earthquake prone location.

Continuous or Spread Footing: This type of foundation is built along the entire length of the wall. The width of the footing is wider than the wall. The load of the structure is effectively spread over a large area. In some countries this type of footing is called wall footing. Footings are typically placed below the frost line. Rebars are highly recommended to add tensile strength to the footing. A step footing is a variation of a spread footing. This system connects all columns and foundation wall making the foundation solid.

Slab on grade foundation: A layer of a minimum of 150 mm to 250 mm thick concrete slab is required. The slab is thicker at the sides for reinforcement bars. A layer of gravel is necessary before as the slab's base course. A mould is set on the ground for the slab to be poured so that there would be no extra space between the ground and the structure. This type of foundation is best for warmer climates where there is frost line to worry about.

Mat Foundation: It has the same dimension of the building so the weight is evenly distributed on the mat. For high rise buildings, piles could have been required before pouring the mat foundation so as to make sure that the soil is compact and dense. Reinforcement bars are placed along the base spaced and sized as specified. A mat foundation could be several metres high when used for high-rise buildings.

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